Semi-constrained bone screw

ABSTRACT

A bone screw for attaching a bone plate to bone includes a shank defining a lumen extending at least partially therethrough from a proximal end thereof, a head defining a lumen therethrough, and a rod member. The rod member is configured for insertion through the lumen of the head and into the lumen of the shank. The rod member is fixedly engageable with the shank and moveably coupled to the head such that both the rod member and the shank are moveable with respect to the head.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 12/940,531, filed on Nov. 5, 2010, which claims the benefit ofand priority to U.S. Provisional Patent Application Ser. No. 61/258,379filed on Nov. 5, 2009, the entire contents of each of which are herebyincorporated by reference herein.

BACKGROUND

1. Technical Field

The present disclosure relates to a bone screw and, more particularly,to a semi-constrained bone screw for use with an implant, such as a boneplate.

2. Background of Related Art

The human spinal column is a highly complex structure. It includes morethan twenty discrete bones, known as vertebrae, coupled sequentially toone another to house and protect critical elements of the nervoussystem. The cervical portion of the spine, which comprises the top ofthe spine up to the base of the skull, includes the first sevenvertebrae.

For many reasons, such as aging and trauma, the intervertebral discs maybegin to deteriorate and weaken, potentially resulting in chronic pain,degenerative disc disease, or even tearing of the disc. Ultimately, thedisc may deteriorate or weaken to the point of tearing and herniation,in which the inner portions of the disc protrude through the tear. Aherniated disc may press against, or pinch, the spinal nerves, therebycausing radiating pain, numbness, tingling, and/or diminished strengthor range of motion.

Many treatments are available to remedy these conditions, includingsurgical procedures in which one or more damaged intervertebral discsare removed and replaced with a prosthetic. However, should theprosthetic protrude from the adjacent vertebrae and thereby contact thesurrounding nerves or tissues, the patient may experience additionaldiscomfort. In procedures for remedying this problem, a spinal plateassembly having one or more apertures and one or more bone screws isaffixed to the vertebrae and oriented to inhibit such protrusion.

A common problem associated with the use of such a spinal plate assemblyis the tendency of the bone screws to “back out” or pull away orotherwise withdraw from the bone into which they are mounted. Thisproblem occurs, primarily, due to the normal torsional and bendingmotions of the body and spine. As the screws become loose and pull awayor withdraw from the bone, the heads of the screws can rise above thesurface of the plate assembly, which results in pain and discomfort forthe patient or possibly the separation of the spinal plate from one ormore vertebrae.

SUMMARY

In accordance with the present disclosure, a bone screw for attaching abone plate to bone is provided. The bone screw includes a shank, a head,and a rod member. The shank has a lumen extending partially therethroughfrom a proximal end of the shank. The head also has a lumen extendingtherethrough. The rod member is configured to be inserted through thelumen of the head and into the lumen of the shank. The rod member isfixedly engageable with the shank and moveably coupled to the head suchthat both the rod member and the shank are moveable with respect to thehead.

In one embodiment, a helical thread is formed on an outer surface of theshank to facilitate insertion of the bone screw into bone.

In another embodiment, the rod member includes a neck portion at adistal end of the rod member. The neck portion is threadably engageablewith an inner surface of the shank.

In yet another embodiment, the rod member includes an outwardlyprotruding annular flange disposed at a proximal end of the neckportion. The annular flange is complementary in shape to an innersurface of the head and is configured to sit on a shoulder positioned onthe inner surface of the head.

In still yet another embodiment, the head is configured to fixedlyengage a bone plate. When the head is engaged with the bone plate, therod member and the shank are moveable with respect to the head and thebone plate.

In still another embodiment, a helical thread is formed on an outersurface of the head for coupling with an opening in the bone plate.

In yet another embodiment, the head is constructed of a material whichis harder than a material of a lip formed in or near the opening in thebone plate.

In accordance with another embodiment of the present disclosure, a boneplate assembly is provided. The bone plate assembly includes a boneplate and one or more bone screws. The bone plate includes a pluralityof openings therein configured for insertion of a bone screwtherethrough. Each bone screw includes a shank, a head, and a rodmember. The shank has an open proximal end and includes a lumenextending partially therethrough. A continuous helical thread isdisposed on an outer surface of the shank. The head has a lumenextending therethrough and includes a plurality of slots defined withinan inner surface of the head. The head is securable within one of theopenings in the bone plate. The rod member includes a distal shaft and aproximal portion. The proximal portion includes a plurality of outwardlyprotruding flanges shaped complementarily to the plurality of slotswithin the inner surface of the head. The distal shaft is insertablethrough the lumen of the head and into the lumen of the shank. Thedistal shaft of the rod member is fixedly engageable with the shank,while the plurality of flanges are configured to sit within theplurality of complementary-shaped slots such that the rod member and theshank are moveable with respect to the head.

In another embodiment, the bone plate includes a plurality of sectionsthat are moveable with respect one another such that the bone plate ismoveable between an expanded and a contracted position. Alternatively,the bone plate may be a unitary structure with fixed dimensions.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the presently disclosed spinal plate and screw assemblyare described herein with reference to the accompanying drawings,wherein:

FIG. 1 is a side view of a bone screw according to an embodiment of thepresent disclosure with parts separated;

FIG. 2 is a side view of the bone screw of FIG. 1 as assembled for use;

FIG. 3 is a side, cross-sectional view of the bone screw of FIG. 1 takenalong section line 3-3 of FIG. 2;

FIG. 4 is an exploded perspective view of the bone screw of FIG. 1;

FIG. 5 is a top view of the head of the bone screw of FIG. 1;

FIG. 6 is a side, cross-sectional view of the head of the bone screw ofFIG. 1 taken along section line 6-6 of FIG. 5;

FIG. 7A is a top perspective view of the head of the bone screw of FIG.1;

FIG. 7B is a bottom perspective view of the head of the bone screw ofFIG. 1;

FIG. 8 is a side view of the shank of the bone screw of FIG. 1;

FIG. 9 is a side, cross-sectional view of the bone screw of FIG. 8,taken along section line 9-9 of FIG. 8;

FIG. 10 is a perspective view of a dynamic bone plate in accordance withone embodiment of the present disclosure; and

FIG. 11 is a perspective view of a bone plate in accordance with anotherembodiment of the present disclosure.

DETAILED DESCRIPTION

Various embodiments of the presently disclosed semi-constrained screwand bone implant (e.g. cervical plate assembly) will now be described indetail with reference to the drawings, wherein like reference numeralsidentify similar or identical elements. In the drawings and in thedescription that follows, the term “proximal,” will refer to the end ofa device or system that is closest to the operator, while the term“distal” will refer to the end of the device or system that is farthestfrom the operator.

Referring initially to FIGS. 1 and 4, bone screw 10 generally includesshank 100, head 200, and rod member 300. Shank 100 includes a distal tipportion 110, an elongated body portion 120, and an open proximal end130. Distal tip portion 110 is generally conically-shaped to facilitateinsertion of bone screw 10 into bone. Elongated body portion 120 ofshank 100 has a substantially uniform outer diameter and includes acontinuous helical thread 122 formed thereon to allow for threadedinsertion and retention of bone screw 10 within bone. A lumen 140 (FIG.3) extends distally from the open proximal end 130 of the shank 100partially therethrough. Head 200 of bone screw 10 is generallyfrustoconical in shape and includes two chambers 230 a and 230 b (FIG.6), the first chamber 230 a having a diameter greater than the diameterof the second chamber 230 b such that a shoulder 234 is defined betweenthe first and second chambers 230 a and 230 b, respectively (FIG. 6). Ahelical threading 222 is disposed on an outer surface 220 of head 200.Further, a plurality of longitudinal slots 232 are defined on an innersurface 231 of first chamber 230 a of head 200, as best seen in FIG. 7A.Rod member 300 of bone screw 10 includes a distal shaft 310, a threadedneck 320, and a proximal flange portion 330 extending radially outwardfrom rod member 300. It is contemplated that the head 200 may be formedfrom a different material than the material of the shank 100 such thatthe bone screw 10 is formed from mixed metals/alloys. Examples ofsuitable materials include titanium, titanium alloys (e.g., Ti-6Al-4V),stainless steel, and cobalt chrome alloys. By way of example only, thehead may be formed of titanium alloy and the shank may be formed ofcommercially pure titanium.

Referring now to FIGS. 2 and 3, helical thread 122 formed on elongatedbody portion 120 of shank 100 is preferably continuous and has asubstantially uniform pitch. Similarly, helical thread 222 on outersurface of head 200 is preferably continuous and has a substantiallyuniform pitch, with the pitch of thread 122 preferably being greaterthan the pitch of thread 222. As best seen in FIGS. 3 and 7B, shank 100and head 200 each include a respective lumen 140, 210. Lumen 140 and theproximal opening of second chamber 230 b may have a substantially equaldiameter and are defined centrally within shank 100 and head 200,respectively. Inner surface of shank 100 includes a threaded portion 142disposed toward a proximal end of lumen 140, while, as discussed above,inner surface 231 of first chamber 230 a of head 200 includes aplurality of longitudinal slots 232 defined therein. As mentioned above,a shoulder 234 is defined between first chamber 230 a and second chamber230 b.

With reference now to FIGS. 1-4, distal shaft 310 of rod member 300 isinsertable through first and second chambers 230 a and 230 b,respectively, of head 200 and into lumen 140 of shank 100. As shaft 310is inserted further through head 200 and into lumen 140, threaded neck320 of shaft 310 is eventually positioned adjacent threaded portion 142of inner surface 141 of shank 100. From this position, rod member 300and shank 100 may be rotated relative to one another to engage threads142 with threads 320 thereby fixedly engaging shank 100 with rod member300. At the same time, proximal flange portion 330 of rod member 300enters first chamber 230 a of head 200. As shown in the drawings,proximal flange portion 330 includes six protrusions 332 defining agenerally hexagonal configuration. Slots 232 defined on inner surface231 of first chamber 230 a of head 200 define a complementary hexagonalshape. Although proximal flange portion 330 is illustrated with sixprotrusions 332, it is contemplated that a greater or lesser number ofprotrusions 332 may be formed in the proximal flange portion 330 with acorresponding number of slots 232 being formed on inner surface 231 ofthe head 200 such that the proximal flange portion 330 and the firstchamber 230 a have complementary configurations. As can be appreciated,the mating of protrusions 332 and slots 232 permits axial translation ofrod member 300 with respect to head 200 along axis X-X, while inhibitingrotation of rod member 300 with respect to head 200 about axis X-X.Shoulder 234, defined between first chamber 230 a and second chamber 230b, acts as a stop, inhibiting rod member 300 from translating furtherdistally through head 200. Accordingly, once rod member 300 is engagedwith shank 100 via the engagement of threads 142 and 320, head 200 isretained therebetween. Although head 200 is retained between shank 100and rod member 300, head portion 200 is axially translatable between afirst position wherein shoulder 234 and proximal flange portion 330 abutone another to inhibit further axial translation in the proximaldirection and a second position wherein a distal portion of head 200contacts the proximal end 120 of shank 100, preventing further axialtranslation in the distal direction. Furthermore, due to theconfiguration of proximal flange portion 330 of rod member 300 and firstchamber 230 a of head 200, rod member 300 and shank 100 are alsomoveable a sufficient distance in the radial direction with respect tohead 200 to accommodate angulation of the shank relative to the head, asdescribed more fully below.

Referring to FIG. 3, shank 100 of bone screw 10 is angularly pivotablerelative to head 200 and longitudinal axis X-X as indicated bydirectional arrows A. Since the diameter of the first chamber 230 a isgreater than an outside diameter of the protrusions 332 of the proximalflange 330 of the rod member 300 and the diameter of second chamber 230b increases from its proximal opening to its distal opening, as describemore fully hereinbelow, rod member 300 is pivotable relative to the head200. A first space is defined between the outer diameter of theprotrusions 332 and the corresponding slots 232, and a second space isdefined between the outer diameter of the proximal flange 330 and innersurface 231 of first chamber 230 a. Additionally, a third space isdefined between an outer surface of elongated body portion 310 (FIG. 4)and an inner surface of second chamber 230 b. The first, second, andthird spaces permit a range of angular movement between rod member 300and head 200 as shown by directional arrows A. Thus, when assembled asbone screw 10, shank 100 is also angularly pivotable relative to head200 as indicated by directional arrows A. In one embodiment, shank 100is pivotable relative to head 200 and axis X-X in a cone with a totalrange of angulation of about 10°. Other ranges of angulation are alsocontemplated.

Although the complementary shaped protrusions 332 and slots 232 of rodmember 300 and head 200, respectively, are described and shown asdefining a hexagonal configuration, it is envisioned that alternateconfigurations may be provided so long as rod member 300 and shank 100are axially translatable and radially moveable, but not rotatable, withrespect to head 200.

Once rod member 300 is threadably engaged with shank 100, with head 200disposed therebetween, as described above, distal end of rod member 300is preferably laser welded to shank 100 along flute cuts 152 of flutes150. One or more windows may be formed through the outer surface of theshank to facilitate laser welding or joining of the rod member 300 andthe shank 100. FIG. 4 illustrates a window extending through a flute,but it is also contemplated that such a welding access window may beformed at any convenient location along the shank to facilitate weldingthe rod to the shank. Alternatively, other techniques for securing therod member 300 and the shank 100 are contemplated. These alternatetechniques include swaging, friction fit (i.e. tapered lumen 140), etc.The laser welding of shank 100 to rod member 300 fixes screw 10 in itsassembled configuration, described above, in which rod member 300 andshank 100 are fixed relative to one another, while head 200 is axiallytranslatable and pivotably movable with respect to shank 100 and rodmember 300 so as to permit angulation between the shank and the head.

Referring to FIGS. 5-7, and as mentioned above, head 200 includes afirst chamber 230 a, having a first diameter, positioned at a proximal,or upper portion of head 200, and a second chamber 230 b, having asecond diameter, positioned at a distal, or lower portion of head 200.The diameter of first chamber 230 a is larger than the diameter of aproximal opening of second chamber 230 b such that a shoulder 234 isdefined therebetween. As shown, the diameter of the first chamber 230 ais substantially uniform between the proximal and distal ends of thefirst chamber 230 a. However, it is contemplated that the proximalopening of first chamber 230 a may have a larger diameter than thedistal opening of first chamber 230 a thus defining a generally conicalor tapered configuration while maintaining the diameter of the distalopening greater than the proximal opening of second chamber 230 b,thereby defining the shoulder 234. A plurality of longitudinal slots 232is defined on inner surface 231 of first chamber 230 a of head 200,extending from the proximal end 202 of head 200 to shoulder 234.Accordingly, as discussed above, the complementary-shaped proximalportion 330 of rod member 300 (FIG. 4) is able to translate throughfirst chamber 230 a of head 200 within slots 232. Proximal portion 330has a smaller diameter than first chamber 230 a but a larger diameterthan the proximal opening of second chamber 230 b such that proximalportion 330 may translate through first chamber 230 a until proximalportion 330 contacts shoulder 234, which inhibits further distaltranslation. The second chamber 230 b has proximal and distal openings.As described hereinabove, the proximal opening of the second chamber 230b has a diameter less than the diameter of the distal opening of thefirst chamber 230 a. Further, the second chamber has a distal openingwith a diameter that is greater than the diameter of the proximalopening of the second chamber 230 a. As shown, the diameter of thesecond chamber 230 b increases from the proximal end near shoulder 234towards the distal end and defines a tapered or chamfered opening. Head200 is preferably constructed of a relatively hard material, such astitanium alloy. More specifically, head 200 may be constructed ofTi-6Al-4V. As best seen in FIG. 6, the width of helical threading 222 onthe outer surface of head 200 tapers slightly from a proximal end 202 toa distal end 204 of head 200, such that head portion 220 is wider at theproximal end 202 as compared to the distal end 204.

Referring now to FIGS. 8-9, the distal end 110 of shank 100 may beconfigured such that bone screw 10 is a “self-starting” or“self-drilling” screw 10. Alternatively, distal end 110 may beconfigured such that bone screw 10 is a “self-tapping” bone screw 10.Further, the bone screw 10 may be configured such that the physicianwould drill and tap a hole in the selected bone structure prior toinserting the bone screw 10. In any configuration, distal end 110includes first and second side walls 154 and 156 that define a flutesection 150 including flute cut 152 (see FIG. 4). The first and secondsidewalls 154, 156 of the flute section 150 extend from the pointed tipportion 110 to a crest of thread 122 near the distal end 110 of shank100. The first sidewall 154 is planar and is aligned along a centrallongitudinal axis “X” of the shank 100 such that first sidewall 154 iscoplanar with the longitudinal axis “X.” The second side wall 156further includes a planar portion that is parallel to the centrallongitudinal axis “X” and an arcuate portion that extends proximallyfrom the planar portion. Similarly, third and fourth side walls (notshown) are defined opposite first and second side walls 154, 156 atdistal end 110 of shank 100. Although not shown in the drawings, theflute defined by the third and fourth side walls also includes a flutecut that is substantially similar to flute portion 150, and isdiametrically opposed to flute portion 150 with respect to longitudinalaxis “X.” As mentioned above, once rod member 300 is inserted andthreadably engaged with shank 100, distal end of rod member 300 is laserwelded to shank 100 along flute cuts 152 of both flutes 150. As bestshown in FIG. 9, central lumen 140 extends distally from open proximalend 120 of shank 100. Lumen 140 extends only partially through shank 100and is dimensioned to have a diameter that is slightly larger than adiameter of elongated body portion 310 of rod member 300 such that rodmember 300 may be disposed therethrough, as shown in FIG. 3.

Referring now to FIG. 10, an implant, such as bone plate 400, is shownhaving a first end section 402 a, a middle section 402 b, and a secondend 402 c. Bone plate 400 is shown in a contracted state, whereinsections 402 a, 402 b and 402 c are in close proximity with one another.Bone plate 400 is adjustable to an expanded state wherein sections 402a, 402 b and 402 c are in a relatively spaced apart position, such thatgaps are defined between the adjacent plate sections. Interlocking teeth408 are separable, to allow for the expansion and retraction of sections402 a, 402 b and 402 c with respect to one another.

Each of plate sections 402 a, 402 b, and 402 c of the bone plate 400 maybe manufactured from commercially pure titanium. In addition, bone plate400 may be available in different configurations (e.g., size, type ofmetal used, etc.) and may be anodized into different colors (e.g.,green, blue, purple, etc.) to indicate the specific configuration of theplate member to the user. Further, depending on the procedure to beperformed, the plate 400 may include more or fewer plate sections 402 a,402 b, 402 c.

Additionally, each of plate sections 402 a, 402 b, and 402 c has aradius of curvature along its longitudinal axis and a radius ofcurvature (e.g., 1.5 inches) along its lateral axis such that the boneplate 400 as a whole may conform to adjacent vertebral bodies of apatient's spine. In instances where the implant (e.g. bone plate 400)spans adjacent bone structures (e.g. vertebral bodies), movement of theadjacent bone structures towards or away from each other is accommodatedby the pivotable (i.e. angular) movement of shank 100 relative to head200. In particular, the pivotable movement of shank 100 relative to head200 allows for normal subsidence in spinal procedures where a bone graftis disposed between adjacent vertebral bodies and the adjacent vertebralbodies move towards each other as the bone graft is assimilated into theadjacent vertebral bodies. Although discussed in terms of a bone plate,the pivotable features of the bone screw 10 are equally applicable withother bone implants such as those where one portion of the implant isfastened or anchored to a fixed location and the bone screw 10 ispositioned at another location on the implant.

The bone plate 400 has a top surface and a bottom surface defining thethickness of the bone plate 400. In addition, bone plate 400 includes aplurality of screw openings 410 and one or more guide openings 420,wherein the screw openings 410 and one or more guide openings 420 extendthrough the thickness of the bone plate 400. The one or more guideopenings 420 are positioned along the central longitudinal axis of thebone plate 400. Each of the screw openings 410 includes a lip 414located on the annular sidewall of the screw opening 410. The lip 414 isconfigured for engaging the head 200 of screw 10 (FIG. 1) such thatthreads 222 of head 200 of screw 10 engage the lip 414. Head 200 may bescrewed into plate 400 until distal end 202 of head 200 is flush withthe top surface of plate 400. It is contemplated that the head 200 maynot be flush with the top surface of the plate 400. As can beappreciated, the increased width of head 200 from distal end 202 toproximal end 204 creates a tighter engagement between head 200 and lip414 as head 200 is threaded, or screwed, into plate 400. Further, sincethe plate 400 (and lip 414) is made of titanium (e.g. commercially puretitanium), a softer material than titanium alloy (e.g. Ti-6Al-4V), whenhead 200 is advanced through screw opening 410, threads 222 of head 200engage the corresponding lip 414 to deform the lip 414 and secure head200 within the screw opening 410. These above-mentioned features helpkeep head 200 fixed within screw opening 410 and inhibit the head 200from backing out of the screw opening 410. This type of screw lockingarrangement is disclosed and shown in U.S. Pat. No. 6,322,562 to Wolter,the entire contents of which are hereby incorporated by referenceherein.

An alternate implant, such as bone plate 500, is shown in FIG. 11. Boneplate 500 has the same essential features as bone plate 400, however,bone plate 500 has a uniform, stationary body 502 that is configured ina one-piece configuration. Bone plate 500 is substantially similar tobone plate 400, other than the fact that bone plate 500 is stationary,rather than expandable. Similarly to bone plate 400, bone plate 500 hasa top surface and a bottom surface, a plurality of screw openings 510and one or more guide openings 520. The screw openings 510 and one ormore guide openings 520 extend through bone plate 500. The one or moreguide openings 520 are positioned along the central longitudinal axis ofthe bone plate 500. Each of the screw openings 510 has a lip 514 locatedtherein in proximity to the bottom surface of the bone plate 500. Lip514, as with lip 414 of plate 400, is configured for engaging a head 200such that rotating the head 200 causes the threads 222 of head 200 toengage and deform the lip 514, fixing head 200 therein. As with boneplate 400, bone plate 500 may be smaller or larger than the bone plate500 shown in FIG. 14, depending on the procedure to be performed. Inorder to provide the advantages of locking engagement between the headmade of a material having greater hardness than the lip, and yet alsoprovide maximal opportunity for material selection choices between thescrew head and plate, it is contemplated that the lip may be provided aspart of an insert into the plate hole. In this manner, the entire plateneed not be made of a material of lower hardness than the screw head. Byway of example, the screw head may be formed of titanium alloy, a platehole insert containing the lip may be formed of commercially puretitanium, and the plate may be formed of PEEK, titanium alloy, cobaltchrome or any other suitable material irrespective of the relativehardness between the screw head and the lip insert.

The operation of bone screw 10 in conjunction with bone plate 400 willnow be described in detail with reference to FIGS. 1-11. Althoughreference hereinbelow is made to bone plate 400, it is contemplated thatthe same operation applies to bone screw 10 in conjunction with plate500 and thus, the description of such will not be repeated. As mentionedabove, during assembly of screw 10, rod 300 is inserted through lumen210 of head 200 and into lumen 140 of shank 100. Rod 300 is then engagedto shank 100 via the engagement of threads 320 with threads 142. Inorder to fix the screw 10 in this configuration, rod member 300 is laserwelded to shank 100 at the flute cuts 152 at distal end 110 of shank100. Once assembled, screw 10 is ready for use.

Initially, plate 400 is adjusted, e.g., plate portions 402 a, 402 b, 402c are moved to the expanded position, according to the size required forthe specific procedure. Next, plate 400 is positioned on the vertebraesuch that bottom side of plate 400 is abutting a surface of bone andsuch that the screw openings 410 are positioned where the screws 10 areto be driven into bone. Distal end of shank 100 of screw 10 is theninserted from the top side of plate 400 and through a screw opening 410in plate 400, such that distal tip 110 of shank 100 is adjacent asurface of bone. A screwdriver, or driving tool (not shown) having acomplementary shape, e.g. hexagonal configuration, to the shape of lumen210 of head 200 is then engaged with head 200. The driving tool (notshown) is then rotated, thereby rotating and driving shank 100 into bonedue to the pitched threading 122 disposed on shank 100. Rotation of thedriving tool (not shown) causes simultaneous rotation of the headportion 200, rod member 300, and shank 100 due to thecomplementary-shaped engagement of the driving tool (not shown) withinner surface 231 of first chamber 230 a of head 200 and due to thecomplementary-shaped engagement of the inner surface 231 with theproximal portion 330 of rod member 300. In other words, the engagementof the driving tool (not shown) and proximal portion 330 of the rodmember 300 allows all the components (shank 100, head 200 and rod member300) of screw 10 to rotate upon rotation of the driving tool (notshown). Alternatively, the physician may prepare the hole using a drilland a tap the hole prior to inserting the bone screw 10.

As the driving tool (not shown) is further rotated to further driveshank 100 into bone, distal end 202 of head 200 eventually enters screwopening 410 of screw plate 400. At this point, further driving of shank100 into bone simultaneously causes head 200 to be driven into screwopening 410. As described above, head 200 is screwed into opening 410via the engagement and deformation of lip 414 with threading 222 onouter surface 220 of head 200. Screw 10 is tightened such that shank 100is secured within bone and such that head portion 200 is secured withinplate 400, as described above. In this position, shank 100 (and thus rodmember 300) is fixedly engaged with bone, and head portion 200 isfixedly engaged with plate 400. However, due to the relationship betweenhead 200 and shank 100 and rod member 300, wherein head 200 is axiallytranslatable and pivotally moveable with respect to shank 100 and rodmember 300, plate 400 is still moveable with respect to bone. In otherwords, plate 400 is not rigidly attached to bone, but, rather, some playexists between plate 400 and bone even though screws 10 are sufficientlysecuring plate 400 to bone.

Insertion of the remaining screws 10 through the respective screwopenings 410 of plate 400 can then be performed as described above,until plate 400 is fully secured to bone.

It will be understood that various modifications may be made to theembodiments of the presently disclosed bone screw. The aforementionedprinciples are applicable to any implant using a bone screw forfastening the implant to bone. In addition, although not preferred, itis contemplated that a thread rather than a lip may be provided in theimplant hole (whether formed in the implant or as part of an insert),such that the threads on the screw head threadably engage threadsprovided in the implant hole. It is further contemplated that othermechanisms could be used in place of the engagement of threads on thescrew head with the lip to secure the screw head to the implant. Thus,additional structures such as a cover plate (whether as a separatestructure applied to the implant or pre-attached to the implant) tocover the screw head and prevent back-out, a set screw to lock the screwhead to the plate and other such structures could be used in place of orin addition to the threaded screw head and lip engagement describedherein and preferred. Therefore, the above description should not beconstrued as limiting, but merely as exemplifications of embodiments.Those skilled in the art will envision other modifications within thescope and spirit of the present disclosure.

What is claimed is:
 1. A method of securing an implant to bone,comprising: providing an implant including at least one openingtherethrough; providing a screw including a shank having an openproximal end and a lumen extending at least partially through the shankfrom the open proximal end, a head having a lumen extending through thehead, and a rod member having a distal shaft and a proximal flange, thedistal shaft extending into and engaged within the lumen of the shank,the proximal flange coupled within the lumen of the head such that thehead is pivotable relative to the shank and rotatably fixed relative tothe shank; and securing the implant to bone by: inserting the screwthrough the opening in the implant; driving the shank into bone; andengaging the head within the opening of the implant, wherein pivotablemovement of the head relative to the shank is permitted with the shankdisposed in bone and the head engaged with the implant.
 2. The methodaccording to claim 1, wherein the shank includes a helical threaddisposed on an outer surface of the shank and wherein driving the shankinto bone includes rotatably driving the shank into bone such that thehelical thread of the shank is engaged within bone.
 3. The methodaccording to claim 2, wherein the head includes a helical threaddisposed on an outer surface of the head and wherein rotatably drivingthe shank into bone effects rotating the head into engagement within theopening of the implant such that the helical thread of the head isengaged within the implant.
 4. The method according to claim 3, whereinat least a portion of driving the shank into bone and engaging the headwithin the opening of the implant is effected simultaneously.
 5. Themethod according to claim 3, wherein an insertion instrument engaged tothe rod member is utilized to rotatably drive the shank into bone and torotate the head into engagement within the opening of the implant. 6.The method according to claim 1, wherein the implant includes a boneplate, the bone plate including a plurality of openings.
 7. The methodaccording to claim 6, wherein securing the implant to bone furthercomprises: inserting a screw through each of the openings in the plate;driving the shank of each screw into bone, at least a first screwengaging a first boney structure and at least a second screw engaging asecond boney structure; and engaging the head of each screw within therespective opening of the plate, whereby relative movement between theboney structures is accommodated by pivoting of the shanks of the firstand second screws relative to the respective heads thereof.
 8. Themethod according to claim 7, wherein the plate includes at least a firstportion and a second portion, the first and second portionsrepositionable relative to one another to permit further relativemovement between the boney structures.
 9. The method according to claim1, wherein the proximal flange includes a plurality of protrusionsextending therefrom and wherein the head includes a plurality ofcomplementary slots defined therein, the protrusions received within theslots to pivotably couple and rotatably fix the shank and head with oneanother.
 10. A method of securing an implant to bone, comprising:providing an implant including at least one opening therethrough;providing a screw including a shank, a head, and a rod member pivotablycoupling the shank and head to one another in fixed rotationalorientation relative to one another; and securing the implant to boneby: inserting the screw through the opening in the implant; rotatablydriving the rod member to both drive the shank into bone and engage thehead within the opening of the implant, wherein pivotable movement ofthe head relative to the shank is permitted with the shank disposed inbone and the head engaged with the implant.
 11. The method according toclaim 10, wherein the shank includes a helical thread disposed on anouter surface of the shank such rotatably driving the rod member engagesthe helical thread of the shank within bone.
 12. The method according toclaim 10, wherein the head includes a helical thread disposed on anouter surface of the head and such that rotatably driving the rod memberengages the helical thread of the head within the implant.
 13. Themethod according to claim 10, wherein at least a portion of driving theshank into bone and engaging the head within the opening of the implantis effected simultaneously.
 14. The method according to claim 10,wherein rotatably driving the rod member includes engaging an insertioninstrument to the rod member and rotatably driving the insertioninstrument.
 15. The method according to claim 10, wherein the implantincludes a bone plate, the bone plate including a plurality of openings.16. The method according to claim 15, wherein securing the implant tobone further comprises: inserting a screw through each of the openingsin the plate; rotatably driving the rod member of each screw to bothdrive the shank into bone and engage the head within the respectiveopening of the implant, at least a first screw engaging a first boneystructure and at least a second screw engaging a second boney structure,whereby relative movement between the boney structures is accommodatedby pivoting of the shanks of the first and second screws relative to therespective heads thereof.
 17. The method according to claim 16, whereinthe plate includes at least a first portion and a second portion, thefirst and second portions repositionable relative to one another topermit further relative movement between the boney structures.
 18. Themethod according to claim 10, wherein the rod member includes a proximalflange having a plurality of protrusions extending therefrom and whereinthe head includes a plurality of complementary slots defined therein,the protrusions received within the slots to pivotably couple androtatably fix the shank and head with one another.